Immune-mediated tissue injury is a primary mechanism of many disease processes that threaten human health. The immune system normally prevents self-injury through numerous control mechanisms, including a reliance on immune regulatory cells. Failure of these control processes can lead to autoimmunity. As a prototypical example of this autoimmune process, Type 1 diabetes (T1D) results from lymphocyte-mediated destruction of insulin-producing islet beta cells. In healthy individuals, the destructive power of the immune system is restrained by specific regulatory cells, but these cells fail to protect individuals with T1D. We propose that interventions to halt Type 1 diabetes and other immune disorders must train the immune system to control itself by restoring normal regulatory T cell function. Unfortunately, it has not been previously possible to rapidly screen candidate therapies to enhance regulatory T cell activation as there has been no biomarker that is unique to activated CD4 Tregs. Although there are markers of activated Tregs, these markers are also expressed by effector T cells; thus, once cells are activated, as is the case for many cells at all times during autoimmunity, it becomes impossible to determine the unique signature of activated Tregs, which confounds any disease-specific screening of Treg enhancing therapy. We have now identified a biomarker GARP that is uniquely expressed by activated CD4 Tregs, have demonstrated its insufficiency in T1D, and have combined this biomarker with other markers of Treg activation to develop a high throughput assay to identify lead compounds to enhance Treg activation. Applying this assay, we will now define new therapies and critical pathways to enhance Treg activation. Using high throughput flow cytometry, we will rapidly determine which compounds and pathways lead to Treg activation (Specific Aim 1). We will also begin translation of these approaches to the clinic by assessing induction of Treg activation in human PBMC's (Aim 1) and by demonstrating biological efficacy in animal models of autoimmune tissue injury and humanized systems (Specific Aim 2). These combined approaches give this application the potential for rapid impact on human diseases resulting from autoimmunity. Overall, our approach will lead to new understanding of the pathways involved in regulatory T cell activation and new pre-clinical approaches for correcting immune regulatory defects by accelerating our discovery of safe, individualized therapies that restore normal regulatory function to the immune system.